JP4483423B2 - Image evaluation method for plasma display panel - Google Patents

Description

  The present invention relates to an image evaluation method for evaluating an image displayed on a plasma display panel.

  The plasma display panel is configured such that a front substrate and a rear substrate are arranged to face each other so that a discharge space is formed therebetween, a peripheral portion is sealed, and a rare gas is sealed in the discharge space. A plurality of display electrodes composed of scan electrodes and sustain electrodes are formed on the front substrate, and a plurality of address electrodes are formed on the rear substrate in a direction orthogonal to the display electrodes. A discharge cell which is a unit light emitting region is formed in the part. In this plasma display panel, a predetermined voltage is applied to the display electrode and the address electrode to generate a discharge selectively in each discharge cell, and the phosphor layer formed in each discharge cell emits light by discharge, An image is displayed.

When manufacturing such a plasma display panel, it is necessary to evaluate the performance of the panel. For example, Patent Document 1 discloses a method for evaluating the performance of a plasma display panel.
JP 11-86731 A

  A plasma display panel is desired to have a uniform display image with no variation in luminance. However, in the actual display image, luminance unevenness occurs because the difference in emission luminance between discharge cells becomes large due to factors such as significant variations in the discharge start voltage in each discharge cell constituting the plasma display panel. If a person views the display image at this time, the display image feels rough. The luminance unevenness referred to here is luminance unevenness caused by a luminance difference for each discharge cell (brightness unevenness in units of discharge cells), and is luminance unevenness generated within a minute range. Such uneven brightness needs to be evaluated in the panel inspection process.

  However, in the actual inspection, there is no method for quantitatively evaluating and inspecting the luminance unevenness of the discharge cell unit, and the inspection of the luminance unevenness of the discharge cell unit has to be performed by the visual evaluation of the inspector. However, the inspection by visual inspection by the inspector is a sensory inspection in which human senses affect the inspection, and the evaluation value may differ depending on the inspector. Also, the evaluation value may vary depending on the physical condition of the inspector, and it is difficult to always perform evaluation based on the same standard.

  The present invention has been made to solve such a problem, and an object of the present invention is to enable appropriate evaluation and inspection of luminance unevenness in discharge cell units generated in a plasma display panel.

In order to achieve such an object, the present invention provides an image evaluation method for a plasma display panel that has a plurality of discharge cells between a pair of substrates and displays an image by generating a discharge in each discharge cell. An image of the plasma display panel is captured by means, the captured image is divided into a plurality of regions, and a ratio between the square root of the unbiased variance of the image data in each of the divided regions and the average value of the image data in each region. And evaluating the image by comparing the evaluation index of the image of the plasma display panel determined in advance using the evaluation index in all the regions and a predetermined evaluation reference value An image evaluation method for a plasma display panel.

  ADVANTAGE OF THE INVENTION According to this invention, the evaluation about the brightness nonuniformity of the discharge cell unit which can generate | occur | produce in a plasma display panel can be performed quantitatively, and the appropriate evaluation and test | inspection about the brightness nonuniformity can be performed.

According to a first aspect of the present invention, there is provided an image evaluation method for a plasma display panel having a plurality of discharge cells between a pair of substrates and displaying an image by generating a discharge in each discharge cell. The image of the plasma display panel is captured by dividing the captured image into a plurality of regions, and the ratio of the square root of the unbiased variance of the image data in each of the divided regions and the average value of the image data in each region. Obtained as an evaluation index, and evaluating the image by comparing the evaluation index of the image of the plasma display panel determined using the evaluation index in all the regions and a predetermined evaluation reference value This is an image evaluation method for a plasma display panel.

Further, the invention according to claim 2 is the invention according to claim 1, wherein a predetermined number or a predetermined ratio of the evaluation indices from the largest value among the evaluation indices in all the regions is set. The average value of the extracted evaluation indices is used as the evaluation index of the image of the plasma display panel .

Further, an invention according to claim 3, in the invention described in claim 1, wherein the image data is image data of three primary colors, and obtains a variation degree of the image data for each color.

Further, the invention according to claim 4, in the invention described in claim 1, wherein the image data is multiplied by the coefficient corresponding respectively to the image data of three primary colors, obtained by adding the data obtained by this multiplication It is characterized by being.

The invention according to claim 5 is the invention according to claim 1, wherein the image data is a product of image data of three primary colors.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  First, the structure of the plasma display panel will be described with reference to FIG. As shown in FIG. 1, the front panel 1 is formed from a dielectric glass so as to form a plurality of display electrode pairs composed of scan electrodes 3 and sustain electrodes 4 on a glass front substrate 2 and to cover the display electrode pairs. The dielectric layer 5 is formed, and the protective layer 6 made of magnesium oxide (MgO) is formed on the dielectric layer 5.

  On the other hand, the back panel 7 disposed opposite to the front panel 1 has a plurality of address electrodes 9 formed on a glass back substrate 8, and a dielectric layer 10 is formed so as to cover the address electrodes 9. A plurality of partition walls 11 parallel to the address electrodes 9 are formed on the body layer 10, and phosphor layers that emit light of red (R), green (G), and blue (B) colors between the adjacent partition walls 11. 12 is formed. The address electrode 9 is located between the adjacent partition walls 11.

  The front substrate 2 and the rear substrate 8 which are a pair of substrates are opposed to each other so that the scan electrodes 3 and the sustain electrodes 4 and the address electrodes 9 are orthogonal to each other, and a peripheral portion of these substrates is a sealing member (not shown). It is sealed using. A discharge gas made of neon and xenon is sealed in a discharge space formed between the front substrate 2 and the rear substrate 8, and a discharge cell is formed at the three-dimensional intersection of the scan electrode 3, the sustain electrode 4 and the address electrode 9. It is formed. That is, a plurality of discharge cells are provided between a pair of substrates. This discharge cell is a unit light emitting region for displaying an image, and one pixel is formed by three adjacent discharge cells formed with phosphor layers 12 that emit light in R, G, and B colors.

  In this plasma display panel, an image is displayed by generating a discharge in each discharge cell. That is, a discharge cell to be displayed is selected by sequentially applying a scan pulse to the scan electrode 3 and applying an address pulse to the address electrode 9 based on the image data, and then alternately maintained on the scan electrode 3 and the sustain electrode 4. By applying a pulse, a sustain discharge is generated in the selected discharge cell. As a result, ultraviolet rays are generated in the discharge cells in which the sustain discharge has occurred, and visible light of each color is emitted from the phosphor layer 12 excited by the ultraviolet rays, and image display is performed.

  Next, a method for evaluating luminance unevenness in units of discharge cells when performing panel inspection on such a plasma display panel will be described. FIG. 2 is an overall configuration diagram of a system that quantitatively evaluates luminance unevenness in units of discharge cells in Embodiment 1 of the present invention.

  As shown in FIG. 2, the plasma display panel 13 to be inspected is mounted on the panel holding unit 14 and driven by the drive circuit 15. The power supply 16 supplies power to the drive circuit 15, and the signal generator 17 supplies signals to the drive circuit 15, and the power supply 16 and the signal generator 17 are controlled by the control device 18. The camera 19 is an image pickup means for picking up an image displayed on the plasma display panel 13, and the pixel of the camera 19 can be measured by at least one pixel with respect to one pixel of the plasma display panel 13. What has resolution is desirable. The image data picked up by the camera 19 is sequentially subjected to data processing by the image conversion circuit 20, the image region dividing circuit 21, and the evaluation index calculation circuit 22, and an evaluation index representing luminance unevenness in units of discharge cells is output.

  FIG. 3 is a flowchart of the evaluation operation algorithm in the first embodiment. As shown in FIG. 3, in the evaluation of luminance unevenness in units of discharge cells, Step 1 for capturing a display image of the plasma display panel 13, Step 2 for converting the captured image, Step 3 for performing region division of the converted image, Step 4 for calculating the evaluation index in each region and step 5 for outputting the evaluation index are sequentially performed.

  First, in step 1, an image corresponding to a signal from the signal generator 17 is displayed on the plasma display panel 13 installed in the panel holding unit 14. Then, an image displayed on the plasma display panel 13 is captured using the camera 19. At this time, if the output data of the camera 19 is represented by 8 bits, the image data R (red data), G (green data), B (blue data) of the three primary colors of the captured image of each pixel of the camera 19 are displayed. Data) is a certain value within the range of 0 to 255. Here, the image displayed on the plasma display panel 13 is, for example, displayed in white by lighting all the discharge cells.

  In the next step 2, the image data R, G, B of the captured image at each pixel of the camera 19 is converted into three types of image data, rR, gG, bB, by the image conversion circuit 20, respectively. It has the values rR, gG, bB. Here, the values of r, g, and b can be arbitrarily set. Here, the values of rR, gG, and bB are normalized so as to be values in the range of 0 to 255, respectively.

  In the next step 3, the image data rR, gG, bB converted by the image conversion circuit 20 is divided into image data of a plurality of areas by the image area dividing circuit 21. FIG. 4 shows an example in which an image captured by the camera 19 and converted by the image conversion circuit 20 (converted image) is divided into 144 areas each having nine vertical columns and sixteen horizontal columns. In FIG. 4, the outer frame 23 represents the image area of the converted image, and the hatched portion 24 represents one of the divided areas. At this time, the value of the image data rR in each divided area has a frequency distribution shown in FIG. 5, for example. Here, the horizontal axis of FIG. 5 represents the value of the image data rR, and the vertical axis represents the number of pixels having the data value in one divided area. The values of the image data gG and bB in each region also have a frequency distribution similar to that in FIG.

In the next step 4, the evaluation index calculation circuit 22 obtains evaluation indexes Zr _i , Zg _i , Zb _i in each region using the values of rR, gG, bB in each divided region. Here, the subscript i is a number representing a region, and when divided into 144 regions as described above, i = 1 to 144. Here, the evaluation indexes Zr _i , Zg _i , and Zb _i are statistical quantities calculated based on the unbiased variance indicating the degree of variation of the statistical data and the average value thereof, and are calculated by the following equation (1).

Here, n is the number of data rR included in the region i, rR _j is image data of each pixel included in the region i, and Σ represents that 1 to n is added to j. Zg _i, similarly to the formula Zr _i also Zb _i, image data gG, is calculated using bB.

In the next step 5, the evaluation indexes Zra, Zga, Zba of the image of the plasma display panel 13 are determined using the evaluation indexes Zr _i , Zg _i , Zb _i in each region calculated by the evaluation index calculation circuit 22. . As a method of determining metrics Zra for red, for example, extracts a 10 metric from those the largest value among the 144 metric Zr _i, and Zra the average value of the ten metric To do. Green, metrics for the blue ZGA, using the same method applies to the ZBA, 144 amino Zg _i respectively, determined using the Zb _i.

  Such evaluation indexes Zra, Zga, Zba are statistics calculated by dividing an image captured by the camera 19 into a plurality of small regions and calculating the unbiased variance indicating the degree of variation of the image data in each region and the average value thereof. Since it is determined based on the amount, it becomes an index representing the luminance unevenness in a small area of the screen of the plasma display panel 13, that is, the luminance unevenness in units of discharge cells. It can be determined that the smaller the values of the evaluation indices Zra, Zga, and Zba, the smaller the luminance unevenness in units of discharge cells, and the better the display quality of the panel.

  According to such an evaluation method, the luminance unevenness of the discharge cell unit can be quantitatively evaluated without depending on the visual evaluation of the inspector, so that the evaluation can always be performed based on the same standard, and the discharge cell unit Appropriate evaluation and inspection can be performed for luminance unevenness. In the panel inspection process, the evaluation index Zra, Zga, Zba is obtained by using the above method, and the quality of the panel is determined by comparing the evaluation index Zra, Zga, Zba with a predetermined evaluation reference value. Will do.

As a method of determining the evaluation indexes Zra, Zga, Zba representing the luminance unevenness in units of discharge cells using the evaluation indexes Zr _i , Zg _i , Zb _i in each region calculated by the evaluation index calculation circuit 22, Arbitrary ratios of evaluation indexes Zr _i , Zg _i , Zb _i are extracted from the upper ranks among the evaluation indexes Zr _i , Zg _i , Zb _i in each region, and the average value of the extracted evaluation indexes is evaluated index Zra , Zga, Zba. Moreover, using a number 1 as an evaluation index in the first embodiment, the evaluation index Zr _i As can be seen from Equation 1 can be omitted Step 2 since a value that is independent of r.

  Next, a method for evaluating luminance unevenness in units of discharge cells in Embodiment 2 of the present invention will be described. The system used in the second embodiment is the same as that shown in FIG. 2, and the evaluation steps are the same as those shown in FIG. Hereinafter, a method for evaluating luminance unevenness in units of discharge cells will be described.

  First, in step 1, an image corresponding to a signal from the signal generator 17 is displayed on the plasma display panel 13 installed in the panel holding unit 14. Then, an image displayed on the plasma display panel 13 is captured using the camera 19. At this time, if the output data of the camera 19 is represented by 8 bits, the image data R (red data), G (green data), and B (blue data) of the captured image in each pixel of the camera 19 are , Each value is in the range of 0-255. Here, the image displayed on the plasma display panel 13 is, for example, displayed in white by lighting all the discharge cells.

  In the next step 2, the image conversion circuit 20 converts the image data R, G, B of the captured image at each pixel of the camera 19 into image data (rR + gG + bB), and each pixel has this value (rR + gG + bB). Have Here, for example, if values r = 1.0000, g = 4.5907, b = 0.0601 are selected, the values can be converted into luminance values in the RGB color system. In addition, the value of rR + gG + bB shall be normalized so that it may become the value of the range of 0-255.

  In the next step 3, the image data rR + gG + bB converted by the image conversion circuit 20 is divided into a plurality of regions by the image region dividing circuit 21. FIG. 4 shows an example in which an image captured by the camera 19 and converted by the image conversion circuit 20 (converted image) is divided into 144 areas each having nine vertical columns and sixteen horizontal columns. In FIG. 4, the outer frame 23 represents the image area of the converted image, and the hatched portion 24 represents one of the divided areas. At this time, the image data rR + gG + bB in each divided area has a frequency distribution similar to that shown in FIG. 5, for example. In FIG. 5, the horizontal axis represents the value of the image data rR + gG + bB, and the vertical axis may be viewed as representing the number of pixels having the data value in one divided area.

In the next step 4, the evaluation index calculation circuit 22 obtains the evaluation index Z _i in each region using the value of rR + gG + bB in each divided region. Here, the subscript i is a number representing a region, and when divided into 144 regions as described above, i = 1 to 144. Here, the evaluation index Z _i is a statistic calculated based on the unbiased variance indicating the degree of variation of the statistical data and the average value thereof, and is calculated by the following equation (2).

Here, n is the number of image data rR + gG + bB included in the region i, (rR + gG + bB) _j is image data of each pixel included in the region i, and Σ is a sum of 1 to n for j. Represents.

In the next step 5, an evaluation index Za representing luminance unevenness in units of discharge cells of the plasma display panel 13 is determined using the evaluation index Z _i in each region calculated by the evaluation index calculation circuit 22. For example, 10 evaluation indexes are extracted from the 144 evaluation indexes Z _i having the largest value, and an average value of the 10 evaluation indexes is set as Za. It can be determined that the smaller the value of the evaluation index Za thus determined, the smaller the luminance unevenness in units of discharge cells, and the better the display quality of the panel.

  According to such an evaluation method, the luminance unevenness of the discharge cell unit can be quantitatively evaluated without depending on the visual evaluation of the inspector, so that the evaluation can always be performed based on the same standard, and the discharge cell unit Appropriate evaluation and inspection can be performed for luminance unevenness. In the panel inspection process, the evaluation index Za is obtained using the above-described method, and the quality of the panel is determined by comparing the evaluation index Za with a predetermined evaluation reference value.

Further, as a method for determining a metric Za by using the evaluation index Z _i in each area calculated by the evaluation index calculating circuit 22, represents luminance non-uniformity of the discharge cell unit, in the evaluation index Z _i in each area Alternatively, an arbitrary ratio of evaluation indices Z _i may be extracted from the top, and the average value of the extracted evaluation indices may be used as the evaluation index Za. In the second embodiment, the image data captured in step 2 is converted into a value of rR + gG + bB, but may be converted into a value of rR × gG × bB, for example.

  In the first and second embodiments, the division of the area shown in FIG. 4 is an example, and in the area division, the evaluation index in each divided area can represent the luminance unevenness in units of discharge cells. The number of areas to be divided and the individual areas of the areas to be divided can be set as appropriate. Further, when the image display area of the plasma display panel 13 cannot be picked up at a time by the camera 19, the image display area of the plasma display panel 13 is divided into a plurality of areas, and the method according to the first and second embodiments for each area May be used.

  As described above, according to the present invention, it is possible to quantitatively evaluate luminance unevenness in discharge cell units that can occur in a plasma display panel, which is useful for inspection of plasma display panels.

The perspective view which shows a part of plasma display panel in one embodiment of this invention 1 is an overall configuration diagram of a system for evaluating brightness unevenness in units of discharge cells according to an embodiment of the present invention. Flow chart of operation algorithm of evaluation in one embodiment of the present invention The figure which shows an example of the division | segmentation of an image area | region The figure which shows the frequency distribution of the image data in the divided area

Explanation of symbols

2 Front substrate 8 Rear substrate 13 Plasma display panel 19 Camera 20 Image conversion circuit 21 Image area dividing circuit 22 Evaluation index calculation circuit

Claims (5)

In an image evaluation method for a plasma display panel that has a plurality of discharge cells between a pair of substrates and displays an image by generating a discharge in each discharge cell, an image of the plasma display panel is picked up by an image pickup means, and the image pickup The obtained image is divided into a plurality of regions, and a ratio between the square root of unbiased variance of the image data in each divided region and the average value of the image data is obtained as an evaluation index in each region, and the above-mentioned in all the regions An image evaluation method for a plasma display panel, comprising: evaluating an image by comparing an evaluation index of an image of the plasma display panel determined using the evaluation index with a predetermined evaluation reference value. A predetermined number or a predetermined proportion of the evaluation indexes are extracted from the evaluation indexes having the largest value among the evaluation indexes in all the regions, and an average value of the extracted evaluation indexes is extracted from the image of the plasma display panel. The image evaluation method for a plasma display panel according to claim 1, wherein the evaluation index is used as an evaluation index. 2. The plasma display panel image evaluation method according to claim 1, wherein the image data is image data of three primary colors, and the degree of variation of the image data is obtained for each color. 2. The image evaluation of a plasma display panel according to claim 1, wherein the image data is obtained by multiplying image data of three primary colors by corresponding coefficients and adding the data obtained by the multiplication. Method. 2. The plasma display panel image evaluation method according to claim 1, wherein the image data is a product of image data of three primary colors.

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